Gas turbine combustor with controlled fuel mixing

ABSTRACT

New combustors, and methods of operating same, which produce lower emissions, particularly lower emissions of nitrogen oxides.

This application is a division of copending application Ser. No.208,137, filed Dec. 15, 1971, now U.S. Pat. No. 3,820,320 issued June28, 1974.

This invention relates to improved gas turbine combustors and methods ofoperating same.

Air pollution has become a major problem in the United States and otherhighly industrialized countries of the world. Consequently, the controland/or reduction of said pollution has become the object of majorresearch and development effort by both governmental and nongovernmentalagencies. Combustion of fossil fuel is a primary source of saidpollution. It has been alleged, and there is supporting evidence, thatautomobiles employing conventional piston-type engines are a majorcontributor to said pollution. Vehicle emission standards have been setby the United States Environmental Protection Agency which aresufficiently restrictive to cause automobile manufacturers to consideremploying alternate engines instead of the conventional piston engine.

The gas turbine engine is being given serious consideration as analternate engine. However, insofar as we presently know, there is nopublished information disclosing realistic and/or practical combustorswhich can be operated at conditions typical of those existing in highperformance engines, and which will have emission levels meeting orreasonably approaching the standards set by said United StatesEnvironmental Protection Agency. This is particularly true with respectto nitrogen oxides emissions.

Thus, there is a need for a combustor of practical and/or realisticdesign which can be operated in a manner such that the emissionstherefrom will meet said standards. Even a practical combustor givingreduced emissions (compared to the combustors of the prior art)approaching said standards would be a great advance in the art. Such acombustor would have great potential value because it is possible thepresently very restrictive standards may be relaxed.

The present invention solves the above-described problems by providingimproved combustors, and methods of operating same, which produceemissions meeting or reasonably approaching the present stringentstandards established by said Environmental Protection Agency.

Thus, according to the invention, there is provided a combustorcomprising, in combination: a flame tube; air inlet means forintroducing a swirling stream of air into the upstream end portion ofsaid flame tube; and fuel inlet means for introducing a stream of fuelinto said flame tube in a direction which is from tangent to less thanperpendicular, but non-parallel, to the periphery of said stream of air.

Further according to the invention, there is provided a method forreducing the amount of nitrogen oxides formed in the combustion of afuel in a cumbustor, which method comprises: introducing a swirlingstream of air into the upstream end portion of a combustion zone as thesole stream of primary air introduced into said combustion zone; formingand introducing an annular stratum of said fuel around said stream ofair by introducing said fuel in a direction toward and which istangential, but non-parallel, to the periphery of said stream of air soas to effect controlled mixing of said fuel and air at the interfacetherebetween to produce an annular fuel-air mixture; passing saidfuel-air mixture into said combustion zone as the sole fuel and airsupplied to the upstream portion of said combustion zone; and burningsaid fuel.

FIG. 1 is a view in cross section of a combustor in accordance with theinvention.

FIG. 1-A is a schematic representation of fuel and air introduction inaccordance with the invention.

FIG. 2 is a cross section taken along the line 2--2 of FIG. 1.

FIGS. 3, 5, and 6 are views in cross section of the flame tube portionof other combustors in accordance with the invention. The outer housingor casing and other elements of these combustors is substantially likethat shown in FIG. 1.

FIG. 4 is a view in cross section taken along the lines 4--4 of FIG. 3.

FIG. 7 is a cross section along the line 7--7 of FIG. 3.

FIGS. 8 and 9 are views in cross section of other closure members ordome members which can be employed with the flame tubes of thecombustors described herein.

Referring now to the drawings wherein like reference numerals areemployed to denote like elements, the invention will be more fullyexplained. In FIG. 1 there is illustrated a combustor in accordance withthe invention, denoted generally by the reference numeral 10, whichcomprises a flame tube 12. Said flame tube 12 is open at its downstreamend, as shown, for communication with a conduit leading to a turbine orother utilization of the combustion gases. A closure member, designatedgenerally by the reference numeral 14, is provided for closing theupstream end of said flame tube. Said closure member can be fabricatedintegrally, i.e., as one element, if desired. However, it is presentlypreferred to fabricate said closure member 14 as two or more elements,e.g., an upstream element 16 and a downstream element 18. An outercasing 20 is disposed concentrically around said flame tube 12 and saidclosure member 14, and spaced apart therefrom to form an annular chamber22 around said flame tube and said closure member. Said annular chamber22 is closed at its downstream end by any suitable means such as thatillustrated. Suitable flange members, as illustrated, are provided atthe downstream end of said flame tube 12 and outer housing 20 formounting same and connecting same to a conduit leading to a turbine orother utilization of the combustion gases from the combustor. Similarly,suitable flange members are provided at the upstream end of said flametube 12 and said outer housing 20 for mounting same and connecting sameto a conduit 24 which leads from a compressor or other source of air.While not shown in the drawing, it will be understood that suitablesupport members are employed for supporting said flame tube 12 and saidclosure member 14 in the outer housing 20 and said upstream end flangemembers. Said supporting members have been omitted so as to simplify thedrawing.

A generally cylindrical swirl chamber 26 is formed in said upstreamelement 16 of closure member 14. The downstream end of said swirlchamber 26 is in open communication with the upstream end of said flametube 12. A first air inlet means is provided for introducing a swirlingmass of air into the upstream end portion of said swirl chamber 26 andthen into the upstream end of said flame tuabe. As illustrated in FIGS.1 and 2, said air inlet means comprises a plurality of air conduits 28extending into said swirl chamber 26 tangentially with respect to theinner wall thereof. Said conduits 28 extend from said annular chamber 22into said swirl chamber 26.

A fuel inlet means is provided for introducing a stream of fuel in adirection which is from tangent to less than perpendicular, butnonparallel, to the periphery of said stream of air. As illustrated inFIGS. 1 and 2, said fuel inlet means comprises a fuel conduit 30 leadingfrom a source of fuel, communicating with a passageway 32, which in turncommunicates with fuel passageway 34 which is formed by an inner wall ofsaid downstream element 18 of closure member 14 and the downstream endwall of said upstream element 16 of closure member 14. It will be notedthat the inner wall of said downstream element is spaced apart from andis complementary in shape to the downstream end wall of said upstreamelement 16. The direction of the exit portion of said fuel passageway 34can be varied over a range which is intermediate or between tangent andperpendicular, but non-parallel, to the periphery of the stream of airexiting from swirl chamber 26. Varying the direction of the exit portionof fuel passageway 34 provides one means or method for controlling thedegree of mixing between the fuel stream and said air stream at theinterface therebetween. As illustrated in FIG. 1, the direction of theexit portion of fuel passageway 34 forms an angle of approximately 45degrees with respect to the periphery of the air exiting from swirlchamber 26. Generally speaking, in most instances, it will be desiredthat the exit portion of said fuel passageway 34 has a direction whichforms an angle within the range of from about 15 to about 75, preferablyabout 30 to about 60, degrees with respect to the periphery of thestream of air exiting from swirl chamber 26. In most instances, it willbe preferred that the fuel from fuel passageway 34 be introduced in agenerally downstream direction. However, it is within the scope of theinvention to introduce said fuel in an upstream direction. Shim 36provides means for varying the width of said fuel passageway 34. Anyother suitable means, such as threads provided on the walls of upstreamelement 16 and downstream element 18, can be provided for varying thewidth of said fuel passageway 34. As will be understood by those skilledin the art in view of this disclosure, the shape of the upstream innerwall of said downstream element 18 and the shape of the downstream endwall of said upstream element 16 can be changed, but maintainedcomplementary with respect to each other, so as to accommodate theabove-described changes in direction and width of said fuel passageway34.

A plurality of openings 38 is provided at a first station in thedownstream portion of said flame tube 12 for admitting a second streamof air into said flame tube from said annular chamber 22. In thecombustor of the invention illustrated in FIG. 1, said second stream ofair will principally comprise quench air for quenching the combustionproducts before passing same on to the turbine.

Referring now to FIG. 3, there is illustrated the flame tube portion andclosure member therefor of another combustor in accordance with theinvention. It will be understood that the complete combustor willcomprise an outer housing or casing 20 and suitable flange memberssubstantially as illustrated in FIG. 1. The flame tube 12' of thecombustor of FIG. 3 is substantially like flame tube 12 of FIG. 1. Aclosure member 40 is mounted on the upstream end of said flame tube 12'in any suitable manner so as to close the upstream end of said flametube except for the openings provided in said closure member. Agenerally cylindrical swirl chamber 42 is formed in said closure member40. The downstream end of said swirl chamber is in open communicationwith the upstream end of said flame tube. An air inlet means is providedfor introducing a swirling mass of air into the upstream end portion ofsaid swirl chamber 42 and then into the upstream end of said flame tube12'. As illustrated in FIGS. 3 and 4, said air inlet means comprises aplurality of air conduits 44 extending into said swirl chamber 42tangentially with respect to the inner wall thereof. Said conduits 44extend from an annular space 22, similarly as in FIG. 1. The fuel inletmeans in the combustor of FIG. 3 comprises a fuel supply conduit 46which is in communication with three fuel passageways 48, which in turnis in communication with an annular fuel passageway 51 formed in thedownstream end portion of said closure member 40. A plurality of fuelconduits 49 extend from said passageway 51 into a recess 50, also formedin the downstream end portion of said closure member, tangentially withrespect to the inner wall of said recess. As illustrated in FIGS. 3 and4, said air inlet conduits 44 are adapted to introduce air tangentiallyinto swirl chamber 42 in a clockwise direction (when lookingdownstream), said fuel inlet conduits 49 in FIG. 7 are adapted tointroduce fuel tangentially into said recess 50 in a counterclockwisedirection. This is a presently preferred arrangement in one embodimentof the invention. However, it is within the scope of the invention toreverse the directions of said air inlet conduits 44 and said fuel inletconduits 49, or to have the directions of both said air inlet conduitsand said fuel inlet conduits the same, e.g., both clockwise or bothcounterclockwise.

Referring now to FIG. 5, there is illustrated the flame tube portion andclosure member therefor of another combustor in accordance with theinvention. The flame tube 52 of the combustor illustrated in FIG. 5 issubstantially like flame tube 12 in FIG. 1 except that the series of airinlet openings 38 has been moved in an upstream direction and a secondplurality of openings 54 has been provided at a second station in thedownstream portion of said flame tube 52, spaced apart from anddownstream from said first plurality of openings 38, for admitting asecond stream of air into the interior of said flame tube from anannular chamber 22 like that shown in FIG. 1 when an outer housing orcasing is provided around said flame tube. Closure member 14 for flametube 52 is like closure member 14 in FIG. 1.

Referring now to FIG. 6, there is illustrated the flame tube portion andclosure member therefor of another combustor in accordance with theinvention. The flame tube 56 of the combustor of FIG. 6 is like flametube 12' of FIG. 3 except that said flame tube 56 has been lengthenedand a second plurality of openings 54 has been provided at a secondstation in the downstream portion of said flame tube, downstream fromand spaced apart from said first plurality of openings 38, for admittinga second stream of air into the interior of said flame tube 56 from anannular space like annular space 22 when an outer housing or casing isprovided around said flame tube, as in FIG. 1. Closure member 40 in FIG.6 is like closure member 40 in FIG. 3.

Referring now to FIGS. 8 and 9, there are illustrated other types ofclosure members which can be employed with the flame tubes of thecombustors described above. In FIG. 8 closure member 78 is similar toclosure member 40 of FIG. 3. The principal difference is that in closuremember 78 a conduit means 80 is provided which extends through saidclosure member 78 into communication with the upstream end portion offlame tube 12, for example. At least one swirl vane 82 is positioned insaid conduit means 80 for imparting a swirling motion to the air passingthrough said conduit means 80. In FIG. 9, closure member 84 is similarto closure member 14 of FIG. 1. The principal difference is that inclosure member 84 an annular conduit means 88 is provided which extendsthrough the body of said closure member 84 into open communication withthe upstream end of the flame tube 12, for example. At least one swirlvane 90 is provided in said conduit means 88 for imparting a swirlingmotion to the air passing through said conduit 88.

In the drawings certain closure members have been employed with certainflame tubes. However, it will be understood that the combustors of theinvention are not limited to the particular combinations illustrated. Itis within the scope of the invention to employ any of the abovedescribed closure members with any of the above described flame tubes.

In one presently preferred method of operating the combustor of FIG. 1,a stream of air from a compressor (not shown) is passed via conduit 24into annular space 22. A portion of said air then passes throughtangential conduits 28 into swirl chamber 26. Said tangential conduits28 impart a helical or swirling motion to the air entering said swirlchamber and exiting therefrom. This swirling motion creates a strongvortex action resulting in a reverse circulation of hot gases withinflame tube 12 upstream toward said swirl chamber 26 during operation ofthe combustor.

A stream of fuel, preferably prevaporized, is admitted via conduit 30,passageway 32, and fuel passageway 34. Fuel exiting from fuel passageway34 is formed into an annular stratum around the swirling stream of airexiting from swirl chamber 26. This method of introducing fuel and aireffects a controlled mixing of said fuel and air at the interfacetherebetween. Initial contact of said fuel and air occurs upon the exitof said air from said swirl chamber 26. Immediately after said initialcontact the fuel and air streams (partially mixed at said interface) areexpanded, in a uniform and graduated manner during passage of said fueland air through the flared portion of member 18, from the volume thereofin the region of said initial contact to the volume of said combustionchamber at a point in said flame tube downstream from said initialcontact. Said expansion of fuel and air thus takes place during at leasta portion of the mixing of said fuel and said air. The resulting mixtureof fuel and air is burned and combustion gases exit the downstream endof flame tube 12. A second stream of air, comprising quench airprincipally, is admitted to the interior of flame tube 12 from annularspace 22 via inlet openings 38 in the downstream portion of said flametube.

In one presently preferred method of operating the combustor of FIG. 3,the method of operation is similar to that described above for thecombustor of FIG. 1. A stream of air is admitted to swirl chamber 42 viatangential inlet conduits 44 which impart a helical or swirling motionto said air. A stream of fuel, preferably prevaporized, is admitted viaconduit 46, fuel passageways 48, and tangential fuel conduits 49 intorecess 50 formed at the downstream end of said closure member 40. Saidfuel is thus formed into an annular stratum around the swirling streamof air exiting from swirl chamber 42. This method of introducing fueland air also effects controlled mixing of said fuel and air at theinterface therebetween.

In one presently preferred method of operating the combustor of FIG. 5,the operation is similar to that described above for the combustor ofFIG. 1. A principal difference is that in addition to the stream of airadmitted from annular space 22 via openings 38 into the interior offlame tube 52, another stream of air is admitted to the interior of saidflame tube via openings 54. The amounts of the various streams of airadmitted through tangential openings 28, openings 38, and openings 54can be controlled by varying and/or correlating the size of saidopenings relative to each other as described further hereinafter inconnection with the examples.

The method of operation of the combustor of FIG. 6 is substantially likethat described above for FIG. 5, taking into consideration that closuremember 40 in FIG. 6 is like closure member 40 in FIG. 3.

The following examples will serve to further illustrate the invention.

EXAMPLES

A series of test runs was made employing combustors of the inventiondescribed herein, and a typical "standard" or prior art combustor as acontrol combustor. The same fuel was used in all of said test runs.Properties of said fuel are set forth in Table I below. Design detailsof the combustors of the invention are set forth in Table II below. Saiddesign details, e.g., dimensions, are given by way of illustration onlyand are not to be construed as limiting the invention. Said dimensionscan be varied within wide limits so long as the improved results of theinvention are obtained. For example, the formation of nitrogen oxides ina combustion zone is an equilibrium reaction. Thus, in designing acombustion zone, attention should be given to the size thereof so as toavoid unduly increasing the residence time therein. It is desirable thatsaid residence time not be long enough to permit the reactions involvedin the formation of nitrogen oxides to attain equilibrium. In said TableII the combustors have been identified by a number which is the same asthe figure number of which they are illustrated.

Said control combustor basically embodies the principal features ofcombustors employed in modern aircraft-turbine engines. It is astraight-through can-type combustor employing fuel atomization by asingle simplex-type nozzle. The combustor liner was fabricated from2-inch pipe, with added internal deflector skirts for air film coolingof surfaces exposed to the flame. Exhaust emissions from this combustor,when operated at comparable conditions for combustion, are in generalagreement with measurements presently available from several differentgas turbine engines. Said control combustor had dimensions generallycomparable to the above described combustors of the invention.

Each of said combustors of the invention and said control combustor wasrun at 12 test points or conditions, i.e., 12 different combinations ofinlet-air temperature, combustor pressure, flow velocity, and heat inputrate. Test points or conditions 1 to 6 simulate idling conditions, andtest points 7 to 12 simulate maximum power conditions. The combustors ofthe invention were run using prevaporized fuel. The control combustorwas run using atomized fuel. Analyses for content of nitrogen oxides(reported as NO), carbon monoxide, and hydrocarbons (reported as carbon)in the combustor exhaust gases were made at each test condition for eachcombustor. Each pollutant measured is reported in terms of pounds per1000 pounds of fuel fed to the combustor. The results from testconditions 1 to 6 are set forth in Table III below. The results fromtest conditions 7 to 12 are set forth in Table IV below.

                  Table I                                                         ______________________________________                                        PHYSICAL AND CHEMICAL PROPERTIES OF TEST FUEL                                                       Philjet A-50                                            ______________________________________                                        ASTM Distillation, F                                                           Initial Boiling Point  340                                                    5 vol % evaporated     359                                                    10 vol % evaporated    362                                                    20 vol % evaporated    371                                                    30 vol % evaporated    376                                                    40 vol % evaporated    387                                                    50 vol % evaporated    398                                                    60 vol % evaporated    409                                                    70 vol % evaporated    424                                                    80 vol % evaporated    442                                                    90 vol % evaporated    461                                                    95 vol % evaporated    474                                                    End Point              496                                                    Residue, vol %         0.8                                                    Loss, vol %            0.0                                                   Gravity, degrees API    46.6                                                  Density, lbs/gal        6.615                                                 Heat of Combustion, net, Btu/lb                                                                       18,670                                                Hydrogen Content, wt %  14.2                                                  Smoke Point, mm         27.2                                                  Sulfur, wt %            0.001                                                 Gum, mg/100 ml          0.0                                                   Composition, vol %                                                             Paraffins              52.8                                                   Cycloparaffins         34.5                                                   Olefins                0.1                                                    Aromatics              12.6                                                  Formula (calculated)    (C.sub.11 H.sub.22)                                   Stoichiometric Fuel/Air Ratio, lb/lb                                                                  0.0676                                                ______________________________________                                    

                                      Table II                                    __________________________________________________________________________    COMBUSTOR DESIGN                                                                                    Combustor Number                                        Variable              1     3     5     6                                     __________________________________________________________________________    Closure Member (14 or 40)                                                      Air Inlet Diameter, in.                                                                            0.875                                                                               1.250                                                                               0.875                                                                               1.250                                   Inlet Type         Tangent                                                                             Tangent                                                                             Tangent                                                                             Tangent                                  Hole Diameter, in.  0.250                                                                               0.281                                                                               0.250                                                                               0.281                                   Number of Holes     6     6     6     6                                       Total Hole Area, sq. in.                                                                          0.295                                                                               0.373                                                                               0.295                                                                               0.373                                   % Total Combustor Hole Area                                                                      10.554                                                                              12.983                                                                               5.571                                                                               6.942                                  Fuel Slot, in.       0.005                                                                               --    0.005                                                                               --                                     Fuel Tube Diameter, in.                                                                            --   12-0.062                                                                             --   12-0.062                                 Exit Type           --   Tangent                                                                              --   Tangent                                Flame Tube                                                                     1st Station (38)                                                               Hole Diameter, in. 5/16×1*                                                                       5/16×1                                                                        5/16×1                                                                        5/16×1                             Total Number of Holes                                                                             8     8     8     8                                       Total Hole Area, sq. in.                                                                          2.500                                                                               2.500                                                                               2.500                                                                               2.500                                   % Total Combustor Hole Area                                                                      89.446                                                                              87.017                                                                              47.214                                                                              46.528                                  2nd Station (54)                                                               Hole Diameter, in.  --    --   5/16×1                                                                        5/16×1                             Total Number of Holes                                                                             --    --    8     8                                       Total Hole Area, sq. in.                                                                          --    --    2.500                                                                               2.500                                   % Total Combustor Hole area                                                                       --    --   47.214                                                                              46.528                                 Total Combustor Hole Area, sq. in.                                                                  2.795                                                                               2.873                                                                               5.295                                                                               5.373                                  Combustor Cross Sect. Area, sq. in.                                                                3.355                                                                               3.355                                                                               3.355                                                                               3.355                                   % Cross Sectional Area                                                                           83.293                                                                              85.616                                                                              157.777                                                                             160.101                                Combustor Inside Diameter, in.                                                                      2.067                                                                               2.067                                                                               2.067                                                                               2.067                                 Primary Zone Length, in.                                                                            7.125                                                                               6.125                                                                               4.625                                                                               6.125                                   Volume, cu. in.    23.909                                                                              20.554                                                                              15.520                                                                              20.554                                 Combustor Length, in.                                                                              11.250                                                                              10.250                                                                              11.250                                                                              12.750                                   Volume, cu. in.    37.751                                                                              34.395                                                                              37.751                                                                              42.784                                 __________________________________________________________________________     *Holes are 5/16" diameter at ends; slots are 1" long.                    

                                      Table III                                   __________________________________________________________________________    COMPARISON OF EMISSIONS FROM COMBUSTORS AT IDLE CONDITIONS                                     Test Conditions                                              Combustor Operating Variables                                                                  1    2   3   4    5   6                                      __________________________________________________________________________    Temperature, Inlet Air, F.                                                                     900  900 900 900  900 900                                    Pressure, in. Hg. abs.                                                                          50   50  50  50   50  50                                    Velocity, Cold Flow, ft/sec.                                                                   250  250 250 400  400 400                                    Heat-Input Rate, Btu/lb Air                                                                    200  275 350 200  275 350                                    NITROGEN OXIDES  lbs/1000 lbs Fuel                                            __________________________________________________________________________    Combustors    No.                                                             Control Combustor                                                                           C  3.4  3.4 3.2   2.2                                                                              2.1 2.3                                    Combustor     1  0.9  0.8 0.9   0.7                                                                              0.6 0.7                                    Combustor     3  5.4  2.3 1.8   3.5                                                                              2.3 1.4                                    Combustor     5  1.3  1.6 2.2   1.0                                                                              1.2 1.2                                    Combustor     6  2.2  1.8 2.2   1.7                                                                              1.5 1.4                                    CARBON MONOXIDE  lbs/1000 lbs Fuel                                            __________________________________________________________________________    Combustors    No.                                                             Control Combustor                                                                           C  10.0 2.0 0.0  17.2                                                                              8.6 0.0                                    Combustor     1  100.2    21.8 1.3 148.0                                                                             36.2                                                                             7.0                                 Combustor     3  70.2 15.2                                                                              0.8  102.6                                                                             50.2                                                                              3.8                                    Combustor     5  24.5 14.2                                                                              0.0  37.6                                                                              18.8                                                                              2.6                                    Combustor     6  15.9 8.9 1.3  26.6                                                                              16.2                                                                              2.6                                    HYDROCARBONS     lbs/1000 lbs Fuel                                            __________________________________________________________________________    Combustors    No.                                                             Control Combustor                                                                           C  0.6  0.7 0.4 0.9  0.4 0.8                                    Combustor     1  0.2  0.2 0.2 0.2  0.2 0.4                                    Combustor     3  0.1  0.1 0.1 0.1  4.8 0.8                                    Combustor     5  0.6  0.1 0.1 0.2  0.1 0.0                                    Combustor     6  0.4  0.3 0.1 0.4  1.0 0.2                                    __________________________________________________________________________

                                      Table IV                                    __________________________________________________________________________    COMPARISON OF EMISSIONS FROM COMBUSTORS                                       AT MAXIMUM POWER CONDITIONS                                                   __________________________________________________________________________                     Test Conditions                                              Combustor Operating Variables                                                                  7   8   9   10  11  12                                       __________________________________________________________________________    Temperature, Inlet Air, F.                                                                     1100                                                                              1100                                                                              1100                                                                              1100                                                                              1100                                                                              1100                                     Pressure, in. Hg abs.                                                                          110 110 110 110 110 110                                      Velocity, Cold Flow, ft/sec                                                                    250 250 250 400 400 400                                      Heat-Input Rate, Btu/lb Air                                                                    150 225 300 150 225 300                                      NITROGEN OXIDES  lbs/1000 lbs Fuel                                            __________________________________________________________________________    Combustors    No.                                                             Control Combustor                                                                           C  10.7                                                                              11.2                                                                              10.0                                                                              9.9 8.0 7.4                                      Combustor     1  6.6 3.4 2.4 6.7 2.0 1.9                                      Combustor     3  26.2                                                                              10.5                                                                              4.4 21.4                                                                              8.2 3.0                                      Combustor     5  4.6 5.3 5.6 2.4 3.4 4.9                                      Combustor     6  8.4 4.7 5.2 10.2                                                                              4.2 4.4                                      CARBON MONOXIDE  lbs/1000 lbs Fuel                                            __________________________________________________________________________    Combustors    No.                                                             Control Combustor                                                                           C  0.0 0.0 0.0 0.0 0.0 0.0                                      Combustor     1  29.6                                                                              5.2 3.0 58.4                                                                              17.3                                                                              4.2                                      Combustor     3  7.2 4.8 19.0                                                                              14.4                                                                              14.0                                                                              0.0                                      Combustor     5  8.4 4.4 0.0 15.1                                                                              4.4 0.0                                      Combustor     6  0.0 0.0 0.0 3.0 0.0 0.0                                      HYDROCARBONS     lbs/1000 lbs Fuel                                            __________________________________________________________________________    Combustors    No.                                                             Control Combustor                                                                           C  0.2 0.1 0.2 0.2 0.2 0.2                                      Combustor     1  0.2 0.2 0.2 0.3 0.2 0.1                                      Combustor     3  0.6 0.8 1.2 1.0 0.6 0.4                                      Combustor     5  0.3 0.3 0.1 0.4 0.2 0.2                                      Combustor     6  0.3 1.0 0.3 2.2 0.2 0.2                                      __________________________________________________________________________

Referring to the above Tables III and Iv, the data there given clearlyshow that all the combustors of the invention gave results superior tothe results obtained with the control combustor. Combustor No. 1 gaveoutstanding results at substantially all test conditions with respect tonitrogen oxides emissions, the pollutant most difficult to control. Saiddata also show that all the combustors of the invention can be operatedat idle conditions to give not more than about 1.8 pounds of nitrogenoxide emissions per 1000 pounds of fuel burned, and not more than about5 pounds of nitrogen oxide emission per 1000 pounds of fuel burned atmaximum power conditions. Such operating conditions would be preferredoperating conditions.

Under some of the test conditions, combustors 1 and 3 tend to give highcarbon monoxide emission. This situation was alleviated by combustors 5and 6 which maintained low levels of nitrogen oxide emissions whilereducing the carbon monoxide emissions. It should be noted that thisresult was obtained by changes which are completely contra to currentconcepts of combustor design. In the operation of combustors 5 and 6 thetotal amount of air to the combustor was maintained constant, e.g., thesame as to combustors 1 and 3. However, the amount of air to the primarycombustion zone of combustors 5 and 6 was decreased by increasing theamount of secondary and/or quench air admitted to the downstream portionof the flame tube. This was accomplished by adding the second set ofinlet slots 54 downstream from the first set of inlet slots 38. This hadthe effect of enriching the primary combustion zone, which wouldincrease carbon monoxide emissions from a typical prior art combustor.

The operation of said combustors 5 and 6 embodies presently preferredmethods in accordance with the invention. In accordance with saidmethods the volume of air utilized as primary air is decreased in anamount sufficient to enrich the fuel to air ratio in the primarycombustion zone, and the volume of the remaining air which is introduceddownstream of the primary combustion zone is increased. Said remainingstream of air of increased volume is divided into a first streamcomprising secondary air and a second stream comprising quench air. Saidfirst stream comprising secondary air is introduced into a first region,e.g., slots 38, downstream from the primary combustion zone and saidstream comprising quench air is introduced into the flame tube of thecombustor at a second region, e.g., slots 54, spaced apart from anddownstream from said first region. In practicing said preferred methodsof the invention, good results have been obtained when the volume of thestream of primary air is decreased by an amount within the range of fromabout 25 to about 75 percent by volume of the volume of primary air atwhich the combustor would normally be operated. The remainder of the airto the combustor is then divided into a stream comprising from about 70to about 30 volume percent thereof and used as said stream comprisingsecondary air, and a stream comprising from about 30 to about 70 volumepercent of said remaining stream of air and used as said streamcomprising quench air.

In the examples, the fuel to the combustors of the invention wasprevaporized. However, the invention is not limited to usingprevaporized fuels. It is within the scope of the invention to employatomized liquid fuels. For comparison purposes, all the runs set forthin the above examples were carried out under the conditions of inlet airtemperature, combustor pressure, flow velocity, and heat input rate setforth in Tables III and IV. The invention is not limited to the valuesthere given for said variables. It is within the scope of the inventionto operate the combustors of the invention under any conditions whichgive the improved results of the invention. For example, it is withinthe scope of the invention to operate said combustors at inlet airtemperatures within the range of from ambient temperatures or lower toabout 1500°F. or higher; at combustor pressures within the range of fromabout 1 to about 40 atmospheres or higher; at flow velocities within therange of from about 1 to about 500 ft. per second or higher; and at heatinput rates within the range of from about 30 to about 1200 BTU perpound of air.

The term "air" is employed generically herein and in the claims, forconvenience, to include air and other combustion supporting gases.

While the invention has been described, in some instances, withparticular reference to combustors employed in combination with gasturbine engines, the invention is not limited thereto. The combustors ofthe invention have utility in other application, e.g., boilers.

While certain embodiments of the invention have been described forillustrative purposes, the invention obviously is not limited thereto.Various other modifications will be apparent to those skilled in the airin view of this disclosure. Such modifications are within the spirit andscope of the invention.

We claim:
 1. A combustor comprising, in combination:a flame tube; airinlet means for introducing a swirling stream of air flowing in adownstream direction into the upstream end portion of said flame tube asthe sole stream of air introduced into said upstream end portion of saidflame tube; and fuel inlet means for forming a sole annular stratum offuel around said stream of air flowing into said flame tube byintroducing said fuel in a direction toward and which is from tangentialto less than perpendicular, but non-parallel, to the periphery of saidstream of air to effect controlled mixing of said fuel and air at theinterface therebetween and produce a sole annular fuel-air mixture forintroduction into said upstream end portion of said flame tube.
 2. Acombustor according to claim 1 wherein said fuel inlet means is adaptedto introduce said fuel in a direction which is intermediate tangent andperpendicular to the periphery of said stream of air.
 3. A combustoraccording to claim 1, comprising, in further combination, meanspositioned downstream from said air inlet means and said fuel inletmeans for causing uniform and graduated expansion of said air and fuelmixture during entry thereof into said flame tube.
 4. A combustoraccording to claim 1 wherein said air inlet means comprises:a swirlchamber disposed at the upstream end of said flame tube, and having adiameter less than the diameter of said flame tube; and conduit meansfor introducing a swirling mass of air into the upstream end portion ofsaid swirl chamber.
 5. A combustor according to claim 4 wherein saidconduit means comprises a plurality of air conduits extending into saidswirl chamber tangentially with respect to the inner wall thereof.
 6. Acombustor according to claim 1 wherein:a closure member is provided forclosing the upstream end of said flame tube; and said air inlet meanscomprises a conduit extending through said closure member intocommunication with the upstream end portion of said flame tube, and atleast one swirl vane positioned in said conduit.
 7. A combustoraccording to claim 6 wherein:a recess is formed in the downstream endportion of said closure member; and said fuel inlet means comprises aplurality of fuel conduits extending into said recess tangentially withrespect to the wall thereof.
 8. A combustor according to claim 6 whereinsaid closure member comprises:an upstream element having said conduitformed therein; a downstream element having formed therein an expansionpassageway which flares outwardly from a point adjacent the downstreamend of said conduit to the inner wall of said flame tube; an inner wallof said downstream element is spaced apart from and is complementary inshape to the downstream end wall of said upstream element so as to forma fuel passageway between said inner wall of said downstream element andthe downstream end wall of said upstream element; and said fuelpassageway communicates with and forms a part of said fuel inlet means.9. A combustor according to claim 8, and further comprising means forvarying the width of said fuel passageway formed between said upstreamand downstream elements of said closure member.
 10. A combustorcomprising, in combination:a flame tube, open at its downstream end; aclosure member closing the upstream end of said flame tube; an outercasing disposed around said flame tube and said closure member andspaced apart therefrom to form an annular chamber around said flame tubeand said closure member, said annular chamber being closed at itsdownstream end; a generally cylindrical swirl chamber formed in saidclosure member, the downstream end of said swirl chamber being in opencommunication with the upstream end of said flame tube; a first airinlet means for introducing a swirling mass of air into the upstream endportion of said swirl chamber and then into the upstream end of saidflame tube as the sole stream of air introduced into said upstream endof said flame tube; and fuel inlet means for forming a sole annularstratum of fuel around said stream of air flowing in a downstreamdirection from said swirl chamber into said flame tube by introducingsaid fuel in a direction toward and which is from tangential to lessthan perpendicular, but non-parallel, to the periphery of said stream ofair to effect controlled mixing of said fuel and air at the interfacetherebetween and produce a sole annular fuel-air mixture, forintroduction into said upstream end portion of said flame tube.
 11. Acombustor according to claim 10 wherein a first plurality of openings isprovided in said flame tube downstream from said closure member foradmitting a second stream of air into said flame tube from said annularchamber.
 12. A combustor according to claim 11 wherein a secondplurality of openings is provided in the downstream portion of saidflame tube, downstream from said first plurality of openings, foradmitting a third stream of air into the interior of said flame tubefrom said annular chamber.
 13. A combustor according to claim 10 whereinthe downstream end portion of said closure member comprises an expansionformed therein and which flares outwardly from a point adjacent thedownstream end of said swirl chamber to the inner wall of said flametube.
 14. A combustor according to claim 13 wherein said closure membercomprises:an upstream element having said swirl chamber formed therein;a downstream element having said expansion passageway formed therein; aninner upstream end wall of said downstream element is spaced apart fromand is complementary in shape to the downstream end wall of saidupstream element so as to form a fuel passageway between said inner wallof said downstream element and the downstream end wall of said upstreamelement; and said fuel passageway communicates with and forms a part ofsaid fuel inlet means.
 15. A combustor according to claim 14 whereinmeans are provided for varying the width of said fuel passageway.
 16. Acombustor according to claim 15 wherein said means for varying the widthof said fuel passageway comprises a shim disposed in said passageway.17. A combustor according to claim 10 wherein said fuel inlet meanscomprises a plurality of conduits extending tangentially through thedownstream end portion of said closure member adjacent the downstreamend of said swirl chamber.
 18. A combustor according to claim 17wherein:said air inlet means comprises a plurality of air conduitsextending into said swirl chamber adjacent the upstream end portionthereof and tangentially with respect to the inner wall thereof; arecess is formed in the downstream end portion of said closure member;and said fuel inlet means comprises a plurality of fuel conduitsextending into said recess tangentially with respect to the wallthereof.
 19. A combustor according to claim 18 wherein said air conduitsextend tangentially into said swirl chamber in one of a clockwise mannerand a counterclockwise manner, and said fuel conduits extendtangentially into said recess in the other of clockwise and saidcounterclockwise manner.